1. The Field of the Invention
This invention relates to internal combustion engines and, more particularly, to novel systems and methods for forced induction systems.
2. The Background Art
It is often desirable to increase the power output of an internal combustion engine. This may be done in several ways. For example, power output can be increased by increasing the displacement of the engine. Generally, however, the larger the displacement, the larger and heavier the engine. Thus, in selected situations, increasing displacement is not an attractive option to obtain a desired increase in power. Accordingly, those of skill in the art have sought ways of increasing power output without increasing displacement.
One method of providing an increase in power output without increasing displacement is to apply a forced induction system to the engine. A forced induction system increases the pressure of intake gases entering the cylinders of the engine. Under greater pressure, more gas molecules (including oxygen molecules) are forced into the cylinders. With the increase in oxygen, greater amounts of fuel may be inserted within the cylinder and combusted to completion. Accordingly, power output may be increased.
Presently, forced inductions systems usually come in one of two forms, superchargers and turbochargers. Superchargers are compressors driven by the crankshaft of the engine. As would be expected, the work done by the compressor is a direct parasitic load on the engine. However, superchargers may still provide a net increase in power so long as the power gain outweighs the parasitic load.
Turbochargers, on the other hand, are not driven directly by the crankshaft of the engine. Instead, a turbocharger uses a turbine to extract energy from the exhaust gases flowing through the exhaust system. This energy is then applied to a compressor that compresses the intake gases. While a turbocharger may require an engine to work harder in expelling exhaust gases, the load on the engine is usually less than that caused by a supercharger. However, unlike superchargers, turbochargers are not instantly responsive to changes in engine speed. Accordingly, turbochargers suffer from what is known as turbo-lag, a delay between the increase in engine speed and the increase in power output.
Typically, the turbine of a turbocharger is surrounded by a scroll (volute). A volute is typically of substantially constantly decreasing cross-sectional area along its length (actually more like a circumference) to maintain substantially a constant gas velocity therein. The scroll acts as a chamber, conduit, and nozzle to direct the flow of exhaust gases toward the surrounded blades of the turbine to induce rotation. Different scrolls are designed for different volumetric flow rates of exhaust gases. The volumetric flow rate of exhaust gases, however, is a function of engine speed. Thus, typical turbocharger turbines operate tn optimal levels only within a specific range of engine speeds. On either side of that specific range, performance of the turbocharger degrades. What is needed is a turbocharger with an adjustable effective scroll volume to properly handle a wider range of volumetric flow rates of exhaust gases.